Power brake boost loss - Maximum Torque Specialists Cadillac Forums

Dave Burden · 08-21-2007, 05:07 PM

When I autocross the '82 Series 75 with a '76 500 under the hood, the boost for the brakes just goes away. It's fairly consistent so I get used to it, but it takes a bit of pressure on the pedal to slow it down. Obviously I'm on the gas a bunch which does not create vacuum, but the two 90's Impalas (5.7) there didn't have a problem.

Under normal driving conditions this doesn't happen, but is there anything I should check?

I checked out a '75 Lincoln Mark IV, that was for sale locally, and saw it uses the power steering pump for the brake boost. Did GM ever use a setup like that?

Dave

Nashalac · 08-21-2007, 05:27 PM

Hydro boost was used on 70's Eldos. Don't know what else. Somebody will post with more knowldge

Schurkey · 08-22-2007, 07:57 AM

1. Verify that the brake booster check valve still works.

2. A bigass vacuum tank--with it's own check valve--will cost a LOT less than a hydroboost system.

3. Hydroboost was extremely common on Diesel pickups. (Diesels don't have any manifold vacuum--although some may have had accessory vacuum pumps.)

thecad · 09-18-2007, 03:50 AM

My 84 GMC 1500 with the 6.2 diesel had hydroboost as well as a step van I had but forget what year it was. The 74 eldo I got my 500 from also had it.

STDog · 09-18-2007, 10:30 AM

Quote:

Originally Posted by Schurkey

1. Verify that the brake booster check valve still works.

2. A bigass vacuum tank--with it's own check valve--will cost a LOT less than a hydroboost system.

I second both those option, in that order.

If the check valve is bad the booster isn't storing vacuum like it should. It should store enough for 3 or 4 applications of the brakes.

Cadillac used storage tanks for the AC system, so the the air control doors didn't move under heavy acceleration/long hills. Without then the active vents/temperature would change under acceleration. My '70 has a send tank that I've never figured out what it was for as well.

So you should be able to find something on a patrs car really cheap. You might even have something already?

Ted in Olympia WA · 09-18-2007, 12:33 PM

Quote:

Originally Posted by Dave Burden

I checked out a '75 Lincoln Mark IV, that was for sale locally, and saw it uses the power steering pump for the brake boost. Did GM ever use a setup like that?

Dave

76-78 Eldorados had the hydro boost system. If you need one I can get one for you, $175 plus shipping for the complete unit. Hydro-boost, lines, power steering pump, even brake pedal if you would like and pump cooler.

But it does make me wonder if there's something wrong with your power brake unit now. Maybe a vacuum tank would work for you.

TED
[email protected]

Dave Burden · 09-18-2007, 01:46 PM

Thanks for all the information. I plan to dig under the hood this week since I have another autocross on Sunday. Right now I'll look at the check valve and see what happens.

Dave

Nashalac · 09-18-2007, 05:16 PM

That's a hell of a deal Ted - wish I needed a system

Ted in Olympia WA · 09-18-2007, 07:52 PM

Maybe I'm selling them too cheap?

If it was me I would go to manual brakes. But maybe he needs power brakes for his kind of hobby?

TED

08-21-2007, 05:07 PM	#1
Dave Burden Member Join Date: May 2005 Location: Central NH Posts: 30	Power brake boost loss When I autocross the '82 Series 75 with a '76 500 under the hood, the boost for the brakes just goes away. It's fairly consistent so I get used to it, but it takes a bit of pressure on the pedal to slow it down. Obviously I'm on the gas a bunch which does not create vacuum, but the two 90's Impalas (5.7) there didn't have a problem. Under normal driving conditions this doesn't happen, but is there anything I should check? I checked out a '75 Lincoln Mark IV, that was for sale locally, and saw it uses the power steering pump for the brake boost. Did GM ever use a setup like that? Dave

08-21-2007, 05:27 PM	#2
Nashalac Senior Member Join Date: Jul 2005 Location: Apple Valley, CA Posts: 743	Hydro boost was used on 70's Eldos. Don't know what else. Somebody will post with more knowldge __________________ MTS for Cadillac quality service

09-18-2007, 05:16 PM	#8
Nashalac Senior Member Join Date: Jul 2005 Location: Apple Valley, CA Posts: 743	That's a hell of a deal Ted - wish I needed a system __________________ MTS for Cadillac quality service

09-18-2007, 07:52 PM	#9
Ted in Olympia WA Senior Member Join Date: May 2005 Location: Olympia WA Posts: 580	\|Hydroboost Maybe I'm selling them too cheap? If it was me I would go to manual brakes. But maybe he needs power brakes for his kind of hobby? TED __________________ Can't never did nothing, Can Do did.

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08-22-2007, 07:57 AM	#3
Schurkey Senior Member Join Date: Mar 2006 Location: The Seasonally Frozen Wastelands Posts: 298	1. Verify that the brake booster check valve still works. 2. A bigass vacuum tank--with it's own check valve--will cost a LOT less than a hydroboost system. 3. Hydroboost was extremely common on Diesel pickups. (Diesels don't have any manifold vacuum--although some may have had accessory vacuum pumps.)

09-18-2007, 03:50 AM	#4
thecad Junior Member Join Date: Jun 2006 Location: Stanwood, Wa. Posts: 3	My 84 GMC 1500 with the 6.2 diesel had hydroboost as well as a step van I had but forget what year it was. The 74 eldo I got my 500 from also had it.

09-18-2007, 01:46 PM	#7
Dave Burden Member Join Date: May 2005 Location: Central NH Posts: 30	Thanks for all the information. I plan to dig under the hood this week since I have another autocross on Sunday. Right now I'll look at the check valve and see what happens. Dave